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AR# 17389

Xtreme DSP Development Kit - Unpredictable ADC and DAC behavior due to external power supply issues

Description

Urgency: Hot

General Description:

The outputs of the analog section of the Xtreme DSP Kit seem to exhibit unpredictable behavior. The digital outputs of the ADCs start to fail, characterized by the reduction in five bits of effective resolution.

Solution

The Xtreme DSP Kit includes an external power supply for using the board over USB. This power supply includes a two meter cable from the power supply to the mini-din connector on the Xtreme DSP Kit mother board. The wire gauge of the two meter cable and its length create a significant voltage drop on the +5V supply at the mother board.

The +5V supply generates the +3.3V and +1.5V supplies on the board. Consequently, depending on the FPGA design and the demand from the generated supplies, a demand is created on the +5V supply lines.

The main issue is that the supply voltage (AVCC) of the AD6644 (14-bit ADCs) is specified as +4.85Vmin. As a result, if there is a significant drop in the +5V across the cable, the voltage may drop below +4.85V. When this occurs, the behavior of the ADC devices is unpredictable.

For more information on this problem, consult the following Application Note:

To resolve this issue, Nallatech will replace your power supply with one that has a larger gauge and a shorter cable to alleviate the voltage drop issue. Please consult the above application note for replacement information.